Following the rapid development of modern electronic industries, the performances of all kinds of electronic components have been rapidly promoted to have faster and faster processing speed. Also, an electronic component contains more and more chips therein. The chips work at high speed and generate high heat at the same time. The heat must be efficiently dissipated outward. Otherwise, the performances of the electronic component will be greatly affected to slow down the processing speed of the electronic component. In some more serious cases, the electronic component may crash or even burn off due to overheating. Therefore, heat dissipation has become a critical topic for all kinds of electronic components. A cooling fan is often used as a heat dissipation device for electronic components.
A conventional axial-flow fan includes a frame body and a fan propeller rotatably mounted in the frame body. In operation, the fan propeller forward rotates within the frame body to transfer air from one side of the fan propeller to the other side thereof so as to dissipate the heat generated by a heat-generating component. However, there are various powder, dust and alien particles (such as suspended particles and fine fluffs) existing in the ambient environment. Therefore, when the axial-flow fan operates, the powder, dust and alien particles will be inevitably entrained by the air to the electronic components of an electronic product. As a result, after a period of use, the blades of the fan propeller will be coated with a considerably thick layer of powder, dust and alien particles. Also, the dust will accumulate over the electronic components of the electronic product. Under such circumstance, the fluid performances of the axial-flow fan will be deteriorated and the heat generated by the electronic components of the electronic product will be dissipated at lower efficiency. Consequently, the performances of the electronic components of the electronic product will be deteriorated and the lifetime of the electronic product will be shortened.
According to the aforesaid, the conventional axial-flow fan has the following shortcomings:    1. The blades of the fan propeller will be coated with a thick layer of dust to affect the fluid performances of the axial-flow fan.    2. The dust is likely to accumulate on the electronic components of the electronic product.    3. The heat dissipation effect is poor.    4. The lifetime is shortened.